“The velocity is still there. Sharpness is there. We check with him all the time,” Nieves said. “He hasn’t shown any of the usual factors. Guys that come from Japan, they throw and throw and throw. He hasn’t shown any fatigue.”

But something is wrong with the usually reliable setup man.

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Tazawa entered a one-run game in the eighth inning on Monday night, put three men on base then committed a terrible fielding blunder as the Los Angeles Angels beat the Red Sox, 4-2, before 35,170 at Fenway Park.

Tazawa has allowed nine runs on 14 hits and seven walks over his last 12⅓ innings. With the Red Sox out of contention, he has pitched in 10 of the 16 games this month. If he is tired, Tazawa has too much personal pride to admit it.

“I don’t feel different physically compared to last year. It’s probably more mental. I’ve been giving up unlucky hits here and there,” he said. “I still appreciate the team using me in a very important role. I try to do my best.”

That strategy looked sound when Howie Kendrick tapped the ball to the left side of the mound. Tazawa had a play at the plate but fumbled the ball then picked it up and threw wildly past catcher Christian Vazquez.

Two runs scored as Tazawa was charged with two errors.

“What looked like a potential inning-ending double play turns into a couple of runs for them,” manager John Farrell said.

Tazawa said he got caught trying to decide whether to backhand the ball.

“If I had knocked it down, I probably had a better shot. It rolled to the third base side and that made it a little more difficult,” he said via translator C.J. Matsumoto. “I should have made that play.”

Nieves believes Tazawa’s problems are a product of familiarity.

“It’s been a tough ride for him,” Nieves said. “The league is starting to realize that he’s a strike-thrower and they don’t want to get to that splitter.”

Adding two runs to the deficit sunk the Sox, who left 12 runners on base and were 1 for 14 with runners in scoring position.

The Nos. 4-7 hitters in the lineup — Yoenis Cespedes, Mike Napoli, Will Middlebrooks, and Xander Bogaerts — were 0 for 16 with two walks and left 15 men on base.

“I thought we had a very good approach offensively, a number of opportunities,” Farrell said.

Red Sox starter Brandon Workman was pitching for the first time since Aug. 9, the night the Red Sox and Angels played 19 innings in Anaheim. Workman came into that game in relief and the first batter he faced, Pujols, belted a walkoff homer.

It was part of a troubling trend. Workman was 0-6 with a 6.35 earned run average in his previous seven games. The Sox decided to skip one turn through the rotation, hoping the time off would help increase Workman’s flagging velocity.

Workman’s fastball didn’t have that much more zip than his last start but he pitched effectively for seven innings, allowing two runs on six hits with two walks and five strikeouts.

The Red Sox put 10 runners on base over 5⅓ innings against Angels starter C.J. Wilson but scored only one run.

Mookie Betts, called up from Triple A Pawtucket to replace Jackie Bradley Jr. in center field, walked with two outs in the fourth inning. Singles by fellow rookies Vazquez and Brock Holt scored Betts. For Holt, it extended his hitting streak to 12 games.

Dustin Pedroia, back in the lineup after sitting out Sunday with an illness, followed with a fly ball to deep center that Trout tracked down.

David Ortiz led off the fifth inning with a double to right field before Cespedes, Napoli, and Middlebrooks went down in order.

Betts singled with one out in the sixth inning, knocking Wilson out of the game. Vazquez followed with a single off Mike Morin and Holt walked to load the bases.

Pedroia had another chance but grounded into his 12th double play of the season. The Red Sox lead the American League with 114.

Wilson (10-8) allowed one run on five hits with five walks and five strikeouts. He had a 9.20 ERA in his previous seven starts as opponents hit .376 against him. A start against the Red Sox fixed that.

Ortiz led off the seventh inning with a single against Fernando Salas. Cespedes, Napoli, and Middlebrooks struck out swinging from there.

The ninth inning was typical of the night’s frustrations. Down, 4-1, after Tazawa’s tumble, Holt led off with a single against Kevin Jepsen and went to third when Pedroia singled.

Ortiz, who had two hits earlier in the game, struck out. Cespedes then grounded into a force at second base as Holt scored. Napoli was next and he lined to center.